1. Field of the Invention
The present invention is in the field of dry abrasive blasting, and more particularly relates to high-performance rotating-nozzle blasting equipment.
2. The Prior Art
The present invention relates to high-performance equipment that moves along the axis of a large pipe while cleaning the interior surface of the pipe by directing a stream of air-suspended dry abrasives at the inside wall of the pipe. The equipment includes a plurality of nozzles directed obliquely outward that rotate about the axis of the pipe.
The high level of performance of the equipment can be appreciated from the fact that in one embodiment the equipment can clean pipes having diameters as large as 32 feet. The apparatus is operated by three men, and the nozzles rotate at approximately 68 revolutions per minute about the axis of the pipe. The apparatus can clean 4,000 square feet per hour to a white metal finish, meaning that all traces of rust, scale, and paint have been removed, leaving only the bare metal.
The equipment can be operated with a wide variety of abrasive particles which are discharged from the nozzles at a velocity of 14,000 feet per second. Abrasive streams of these velocities are highly destructive of the blasting machine unless the machine is specifically designed to avoid excessive wear. Such machines are expensive to operate, and because they interfere with other operations on the pipe being cleaned, it is important that the cleaning job be finished as rapidly as possible. Consequently, high reliability and minimum down-time were important considerations in the design. The present application describes several design innovations that have resulted in operating times of at least 1,000 hours without interruptions. This is clearly good performance for a machine that handles such highly abrasive streams.
In U.S. Pat. No. 2,358,557, Boyd el al. describe a blast cleaning device having a rotating nozzle head and in which the bearings of the rotating nozzle head are protected from invasion by the abrasive material through the use of a seal and bleeder ducts to prevent circulation of the pressurized air through the bearings.
In U.S. Pat. No. 5,113,885, Ramsey shows a pipe cleaning apparatus having a rotating nozzle head that is mounted in a bushing that is sealed.
In U.S. Pat. No. 5,020,188, Walton describes an apparatus for cleaning the interior of ductwork from within, but the problems addressed by the present invention are not discussed by Walton.
In U.S. Pat. No. 4,690,159, Vadakin et al. describe a rotary cleaning device that rides along a cable within the pipe to be cleaned. O-rings are used to prevent the pressurized fluid from leaking, but the problems solved by the present invention are not discussed.
In U.S. Pat. No. 3,987,963, Pacht shows a hand-held lance having a rotating sprayhead.
The equipment of the present invention combines extremely high performance with very good reliability and minimum downtime. This high degree of performance is attributable to certain design features to be discussed below, which in the light of the known prior art believed to be novel and innovative.